The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A balance shaft is a device for reducing vibration and noise generated by the reciprocating motion of a piston and the rotary motion of a crankshaft when an engine rotates. That is, the balance shaft rotates in a direction opposite to the crankshaft so as to cancel out vibration and noise generated by the rotary motion of the crankshaft. A mechanical balance shaft and a motor-driven balance shaft are used as examples of such a balance shaft.
Since the mechanical balance shaft is connected to the crankshaft of an engine by chains, gears, or the like, it is always driven regardless of an engine speed. However, the balance shaft requires a high engine speed equal to or higher than 4000 RPM, at which inertial force due to the reciprocating mass of the engine, e.g. a piston, is rapidly increased. For this reason, if the balance shaft is always driven, fuel efficiency may be very poor.
In order to address this issue, the motor-driven balance shaft, which is driven only in a high engine speed range by controlling the operation of a motor, is developed. However, the motor-driven balance shaft requires a separate motor, a motor control unit, and a power supply. For this reason, there is an issue in that the cost and weight of the balance shaft are increased and a separate space must be provided within an engine room.
In addition, since a starter motor for an ISG (Idle Stop and Go) system is used only to start or restart an engine, it is rarely utilized.